Semiconductor device and semiconductor package

ABSTRACT

A semiconductor device capable of ensuring a withstand voltage of a transistor and reducing a forward voltage of a Schottky barrier diode in a package with the transistor and the Schottky barrier diode formed on chip, and a semiconductor package formed by a resin package covering the semiconductor device are provided. The semiconductor device  1  includes a semiconductor layer  22 , a transistor area D formed on the semiconductor layer  22  and constituting the transistor  11 , and a diode area C formed on the semiconductor layer  22  and constituting the Schottky barrier diode  10 . The semiconductor layer  22  in the diode area C is thinner than the semiconductor layer  22  in the transistor area D.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and asemiconductor package formed by a resin package covering thesemiconductor device.

2. Description of the Related Art

The semiconductor device disclosed in Patent Document 1 contains aSchottky barrier diode connected between a source and a drain. Inparticular, a p-type base layer is formed on a surface portion of ann-type semiconductor layer stacked on an n-type semiconductor substrateof the semiconductor device. A trench is dug from the surface of then-type semiconductor layer and penetrates through the p-type base layer,and a gate insulating film is formed on the sidewall and the bottom ofthe trench. A gate electrode is embedded in the trench. An n-typediffusion layer is formed on the surface portion of the p-type baselayer.

A trench gate-type transistor is thereby formed in the semiconductordevice. In the transistor, the n-type diffusion layer is a source area,and the n-type semiconductor layer is a drain area. A channel is formednear an interface of the p-type base layer and the gate insulating filmbetween the n-type diffusion layer and the n-type semiconductor layer,so that a current passes between the source area and the drain.

A metal layer is stacked on the surface of the n-type semiconductorlayer. The metal layer exerts the function of source electrode by meansof contacting the n-type diffusion layer and forming the Schottkybonding between the area and the metal layer by means of contacting thearea outside the p-type base layer and the surface of the n-typesemiconductor layer. In this manner, the transistor and the Schottkybarrier diode are formed on one chip in the semiconductor device.

-   Patent Document 1: Japanese Laid-open Patent Publication No.    2009-59860

SUMMARY OF THE INVENTION

To ensure a (certain) withstand voltage of a transistor, the thicknessof an n-type semiconductor layer is required to be greater than anecessary thickness. In the semiconductor device of Patent Document 1,the thickness of the n-type semiconductor layer in the area where thetransistor is formed is the same as the area where a Schottky barrierdiode is formed. Therefore, although the withstand voltage of thetransistor is guaranteed, the thickness of the n-type semiconductorlayer in the Schottky barrier diode area is required to be higher than anecessary thickness, so the DC resistance of the Schottky barrier diodeincreases. Therefore, a forward voltage (VF) of a Schottky barrier diodeis difficult to reduce.

Therefore, the present invention is directed to providing asemiconductor device capable of ensuring a withstand voltage of atransistor and reducing a forward voltage of a Schottky barrier diode ina package with the transistor and the Schottky barrier diode formed on achip, and a semiconductor package formed by a resin package covering thesemiconductor device.

The semiconductor device of the present invention includes asemiconductor layer, a transistor area formed on the semiconductor layerto constitute the transistor, and a diode area formed on thesemiconductor layer to constitute the Schottky barrier diode. Thesemiconductor layer in the diode area is thinner than the semiconductorlayer in the transistor area (technical solution 1).

In the transistor area, the thickness of the semiconductor layer isdesigned to be a thickness necessary to ensure the withstand voltage ofthe transistor. On the other hand, the thickness of the semiconductorlayer in the diode area is set to be a minimum necessary level. A DCresistance of the Schottky barrier diode may be reduced this way,thereby reducing the forward voltage. That is to say, the thickness ofthe semiconductor layer in the transistor area and the diode area areeach optimized. Therefore, the transistor and the Schottky barrier diodeformed on the chip ensure the withstand voltage of the transistor isensured and reduce the forward voltage of the Schottky barrier diode.

Preferably, the semiconductor layer in the diode area is 1 μm or morethinner than the semiconductor layer in the transistor area (technicalsolution 2).

Preferably, the thickness of the semiconductor layer in the diode areais 2.5 μm or more (technical solution 3).

According to the present composition, a minimum level withstand voltageof the Schottky barrier diode can be ensured.

Preferably, when the transistor is a trench-type transistor having afirst trench dug from a surface of the semiconductor layer in thetransistor area, the bottom of the first trench and the surface of thesemiconductor layer in the diode area are located at the same positionin a thickness direction of the semiconductor layer (technical solution4).

According to the present composition, the steps of forming the firsttrench and polishing the semiconductor layer in the diode area from thesurface side to make the semiconductor layer thinner may be carried outin one step. Reducing the number of steps lowers the cost of fabricatingthe semiconductor device. In this manner, an inexpensivehigh-performance semiconductor device can be provided.

However, in the thickness direction of the semiconductor layer, ascompared with the surface of the semiconductor layer in the diode area,the bottom of the first trench may also be located at a position furtheraway from a back surface of the semiconductor layer (technical solution5), and may also be located at a position closer to the back surface ofthe semiconductor layer (technical solution 6).

Preferably, the depth of the first trench is 1 μm or more (technicalsolution 7).

Preferably, a SiO₂-containing gate insulating film is formed on an innersurface of the first trench (technical solution 8). Preferably, apolysilicon-containing gate electrode is embedded on an inner side ofthe gate insulating film of the first trench (technical solution 9).

Preferably, when the transistor includes a main area, a drain area and asource area, a second trench in contact with the source area is formedon the semiconductor layer. The second trench is dug from a surface ofthe semiconductor layer in the transistor area and the surface of thesemiconductor layer in the diode area is located at a position deeperthan the bottom of the second trench (technical solution 10).

Preferably, the first trench and the second trench are alternatelyconfigured as shown in vertical view along the thickness direction ofthe semiconductor layer (technical solution 11). In this situation, thefirst trench and the second trench may be stripe-shaped (technicalsolution 12), or the first trench may be mesh-shaped as a mesh-shapedarea on which the second trench is configured on an inner side thereof(technical solution 13).

The transistor may also be a planar transistor (technical solution 14).

Preferably, the transistor area surrounds the diode area as shown invertical view along the thickness direction of the semiconductor layer(technical solution 15).

When the transistor of the transistor area is ON, the Schottky barrierdiode of the diode area is OFF, thereby realizing heat dissipation ofthe semiconductor layer by using the diode area. When the transistor isOFF, heat dissipation of the semiconductor layer may be realized byusing the transistor area. The above manner may prevent the temperatureof the semiconductor device from rising. In particular, the transistorarea is configured to surround the diode area, so as to dissipate theheat of one area by means of another area, thereby effectivelypreventing the temperature of the semiconductor device from rising. Whenmultiple diode areas exist, the diode areas are scattered and uniformlydistributed at a necessary interval, thus further effectively preventingthe temperature of the semiconductor device from rising.

Preferably, the semiconductor device further includes a metal film. Themetal film is electrically connected with the transistor and Schottkybonded with the semiconductor layer in the diode area (technicalsolution 16). In this situation, the metal film preferably contains Ti,Mo, Pd or TiN (technical solution 17).

Preferably, the semiconductor layer is epitaxially grown on a surface ofa semiconductor substrate (technical solution 18).

Preferably, the semiconductor device further includes a back surfaceelectrode. The back surface electrode is in ohmic contact with a backsurface of the semiconductor substrate (technical solution 19).

The semiconductor package of the present invention includes thesemiconductor device and a resin package covering the semiconductordevice (technical solution 20).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described according to the appended drawings, inwhich:

FIG. 1 is a schematic plan view of a semiconductor device according toan embodiment of the present invention;

FIG. 2 is a schematic plan view of a semiconductor device according toanother embodiment of the present invention;

FIG. 3 is an enlarged view of the main portions of the semiconductordevice in FIG. 1 or FIG. 2;

FIG. 4 is a schematic view of a variant embodiment of the main portionsof the semiconductor device in FIG. 3;

FIG. 5 is a cross-sectional view taken along a cutting line V-V in FIG.3 or FIG. 4;

FIG. 6A is an illustrative cross-sectional view of a fabricating methodof the semiconductor device in FIG. 5;

FIG. 6B is an illustrative cross-sectional view of a step subsequent toFIG. 6A;

FIG. 6C is an illustrative cross-sectional view of a step subsequent toFIG. 6B;

FIG. 6D is an illustrative cross-sectional view of a step subsequent toFIG. 6C;

FIG. 6E is an illustrative cross-sectional view of a step subsequent toFIG. 6D;

FIG. 6F is an illustrative cross-sectional view of a step subsequent toFIG. 6E;

FIG. 6G is an illustrative cross-sectional view of a step subsequent toFIG. 6F;

FIG. 6H is an illustrative cross-sectional view of a step subsequent toFIG. 6G;

FIG. 6I is an illustrative cross-sectional view of a step subsequent toFIG. 6H;

FIG. 6J is an illustrative cross-sectional view of a step subsequent toFIG. 6I;

FIG. 6K is an illustrative cross-sectional view of a step subsequent toFIG. 6J;

FIG. 6L is an illustrative cross-sectional view of a step subsequent toFIG. 6K;

FIG. 6M is an illustrative cross-sectional view of a step subsequent toFIG. 6L;

FIG. 7 is an illustrative cross-sectional view of a semiconductor deviceaccording to another embodiment of the present invention;

FIG. 8 is an illustrative cross-sectional view of a semiconductor deviceaccording to another embodiment of the present invention;

FIG. 9 is a schematic perspective view of a semiconductor packageaccording to an embodiment of the present invention; and

FIG. 10 is a circuit diagram of a DC-DC converter adopting thesemiconductor device of the present invention.

LIST OF REFERENCE NUMERALS

-   -   1 semiconductor device    -   10 Schottky barrier diode    -   11 transistor    -   12 first trench    -   12A bottom    -   13 second trench    -   13A bottom    -   21 back surface electrode    -   22 semiconductor layer    -   22A surface    -   22B back surface    -   23 gate insulating film    -   24 gate electrode    -   27 first metal film    -   31 p⁻-type semiconductor layer    -   32 n⁺-type semiconductor layer    -   34 n⁻-type semiconductor layer    -   41 metal film    -   53 metal film    -   60 semiconductor package    -   65 resin package    -   C diode area    -   D transistor area

PREFERRED EMBODIMENT OF THE PRESENT INVENTION

Hereinafter, the embodiments of the present invention will beillustrated in detail with reference to the drawings.

FIG. 1 is a schematic plan view of a semiconductor device according toan embodiment of the present invention. FIG. 2 is a schematic plan viewof a semiconductor device according to another embodiment of the presentinvention.

In an embodiment of the present invention, the semiconductor device 1 isin the shape of a quadrilateral chip when observed from the top. Each offour sides of the semiconductor device 1 when observed from the top hasa length for example of several millimeters.

On the quadrilateral surface of the semiconductor device 1 when observedfrom the top, an external connection area A is formed along one side,and a movable area B is formed in the area outside the externalconnection area A. The semiconductor device 1 has: a plurality ofexternal electrodes 2 configured in the external connection area A; aretaining ring 3 surrounding the movable area B; a plurality of diodeareas C configured in the movable area B; and a transistor area D in themovable area B except the diode area C.

A plurality of (7 herein) external electrodes 2 is arranged along oneside of the quadrilateral. Each of the external electrodes 2 isconnected to the lead (not shown) by a connecting line (not shown) (seethe description that follows below). The retaining ring 3 insulates andseparates the external connection area A and the movable area B.

A plurality of diode areas C is scattered (discrete-configured)uniformly in the movable area B. In particular, a plurality of diodeareas C may be spaced at an interval and arranged in a zigzag shape inFIG. 1 or a matrix shape in FIG. 2.

FIG. 3 is an enlarged view of the main portions of the semiconductordevice in FIG. 1 or FIG. 2. FIG. 4 is a schematic view of a variantembodiment of the main portions of the semiconductor device in FIG. 3.

FIG. 3 illustrates the part enclosed by dashed line in FIG. 1 or FIG. 2(one diode area C and the surrounding transistor area D thereof).

Each diode area C is square-shaped when observed from the top. Whenobserved from the top, each diode area C is surrounded by the transistorarea D.

A Schottky barrier diode 10 is formed in the diode area C, and aplurality of transistor units 11A is formed in the transistor area D.The plurality of transistor units 11A are connected to one another toform one transistor 11 (see FIG. 1). The transistor 11 contains aplurality of Schottky barrier diodes 10 (see FIG. 1). In this manner,the transistor 11 is formed surrounding a plurality of Schottky barrierdiodes 10 in the movable area B of the semiconductor device 1 (see FIG.1).

Regarding the plurality of transistor units 11A (transistor 11), thefirst trench 12 and the second trench 13 are dug substantially in theoverall surface area (i.e., the surface of the semiconductor layer 22)of the semiconductor device 1 of the transistor area D. The first trench12 and the second trench 13 extend straight in the first direction Ywhen observed from the top, and are configured alternately at aninterval in the second direction X perpendicular to the first directionY. In other words, the first trench 12 and the second trench 13 arerespectively stripe-shaped.

For the first trench 12 and the second trench 13, the second trench 13is further formed at the position closest to the diode area C as aquadrilateral loop surrounding the entire diode area C. The first trench12 adjacent to the second trench 13 located at the position closest tothe diode area C is a quadrilateral loop surrounding the entire secondtrench 13.

The configuration of the first trench 12 and the second trench 13 mayfurther refer to that shown in FIG. 4. The first trench 12 may bedivided into a plurality of rectangular mesh-shaped areas by themesh-shaped pattern. In each rectangular mesh-shaped area, the secondtrench 13 is spaced at an interval relative to the first trench 12 andextends straight. In this situation, the second trench 13 located at theposition closest to the diode area C is a quadrilateral loop surroundingthe entire diode area C, and the first trench 12 adjacent to the secondtrench 13 is a quadrilateral loop surrounding the entire second trench13.

FIG. 5 is a cross-sectional view taken along a cutting line V-V in FIG.3 or FIG. 4.

As shown in FIG. 5, the semiconductor device 1 has a semiconductorsubstrate 20, a back surface electrode 21, a semiconductor layer 22, agate insulating film 23, a gate electrode 24, an oxide film 25, aninsulating layer 26, a first metal film 27, a second metal film 29, asource electrode 28 and a wiring layer 30.

The semiconductor substrate 20 includes an n⁺-type semiconductor (e.g.silicon).

The back surface electrode 21 covers the entire back surface (the lowersurface in FIG. 5) of the semiconductor substrate 20. The back surfaceelectrode 21 includes a metal (e.g. Ag, NiSi, CoSi) in ohmic contactwith the n-type silicon. Therefore, the back surface electrode 21 is inohmic contact with the back surface of the semiconductor substrate 20.

The semiconductor layer 22 is stacked on the surface (the upper surfacein FIG. 5) of the semiconductor substrate 20. The semiconductor layer 22includes an n⁻-type semiconductor having a concentration lower than thesemiconductor substrate 20. In the semiconductor layer 22 in FIG. 5, theupper surface is referred to as the surface 22A, and the lower surfaceis referred to as the back surface 22B. The thickness of the entiresemiconductor layer 22 is, for example, 4 μm.

The semiconductor layer 22 is formed on the diode area C and thetransistor area D.

FIG. 5 shows the semiconductor layer 22 around the boundary of the diodearea C and the transistor area D. The semiconductor layer 22 of thediode area C is thinner than the semiconductor layer 22 in thetransistor area D. Therefore, the surface 22A of the semiconductor layer22 in the diode area C is located at a position deeper and closer to thesemiconductor substrate 20 as compared with the surface 22A of thesemiconductor layer 22 in the transistor area D. Therefore, the surface22A of the semiconductor layer 22 in the diode area C is recessedtowards the semiconductor substrate 20. On the other hand, the backsurface 22B of the semiconductor layer 22 is flat and covers the entirearea of the diode area C and the transistor area D, and extends parallelto the surface 22A of the semiconductor layer 22.

The interval between the surface 22A and the back surface 22B of thesemiconductor layer 22 in the transistor area D is referred to as theinterval P. The interval between the surface 22A and the back surface22B of the semiconductor layer 22 in the diode area C is referred to asthe interval Q. The interval P is the thickness of the semiconductorlayer 22 in the transistor area D. The interval Q is the thickness ofthe semiconductor layer 22 in the diode area C. The interval P is largerthan the interval Q. The difference between the interval P and theinterval Q is, for example, 1 μm or more. In other words, thesemiconductor layer 22 in the diode area C is 1 μm or more thinner thanthe semiconductor layer 22 in the transistor area D.

On the entire surface portion of the semiconductor layer 22 in thetransistor area D, a p⁻-type semiconductor layer 31 is formed. The areacloser to the back surface 22B as compared with the p⁻-typesemiconductor layer 31 on the semiconductor layer 22 is the n⁻-typesemiconductor layer 34. The n⁺-type semiconductor layer 32 isselectively formed on the surface portion of the p⁻-type semiconductorlayer 31. On the surface of the n⁺-type semiconductor layer 32, in thesame plane of the surface of the p⁻-type semiconductor layer 31 wherethe n⁺-type semiconductor layer 32 is not formed, the surface 22A of thesemiconductor layer 22 in the transistor area D is formed.

The first trench 12 is formed on the semiconductor layer 22 in thetransistor area D. The first trench 12 is dug from the surface 22A tothe back surface 22B of the semiconductor layer 22 in the transistorarea D. The first trench 12 penetrates through both the n⁺-typesemiconductor layer 32 and the p⁻-type semiconductor layer 31 to reachthe middle thickness of the n⁻-type semiconductor layer 34. The intervalR between the bottom 12A (bottom 12A indicated by the solid line) of thefirst trench 12 and the back surface 22B of the semiconductor layer 22is smaller than the interval P, and is equal to the interval Q. In otherwords, the bottom 12A of the first trench 12 and the surface 22A of thesemiconductor layer 22 in the diode area C are located at the same levelof thickness of the semiconductor layer 22, and thus are located in thesame plane. The depth of the first trench 12 is, for example, 1 μm ormore.

The gate insulating film 23 contains SiO₂ and is connected to the entireinner surface (the sidewall and the bottom) of the first trench 12.

The gate electrode 24 contains, for example, polysilicon. The gateelectrode 24 is embedded in the inner side of the gate insulating film23 in the first trench 12.

The oxide film 25 contains SiO₂, and covers substantially the entiresurface 22A of the semiconductor layer 22 in the transistor area D.

The insulating layer 26 contains a glass like BPSG (Boron PhosphorSilicate Glass), and is stacked on the oxide film 25.

The second trench 13 is dug from the surface (the upper surface inFIG. 1) of the insulating layer 26, penetrates through the insulatinglayer 26 and the oxide film 25, and penetrates through n⁺-typesemiconductor layer 32 in the semiconductor layer 22 to reach the middlethickness of the p⁻-type semiconductor layer 31. The second trench 13 islocated on the semiconductor layer 22 in the transistor area D, and isformed at a position other than the first trench 12, and is dug from thesurface 22A of the semiconductor layer 22 at the position. The intervalS between the bottom 13A of the second trench 13 and the back surface22B of the semiconductor layer 22 is smaller than the interval P, and islarger than the interval Q and the interval R. In other words, thesurface 22A of the semiconductor layer 22 in the diode area C is locatedat a deeper position than the bottom 13A of the second trench 13.

The p⁺-type semiconductor layer 33 surrounds the second trench 13 of thep⁻-type semiconductor layer 31.

The first metal film 27 includes a Schottky bonded metal (e.g. Ti, Mo,Pd or TiN) formed by bonding with the n⁻-type silicon. The first metalfilm 27 is connected with the entire inner surface of the second trench13, and in this state, is electrically connected (in ohmic contact) withthe n⁺-type semiconductor layer 32 and the p⁺-type semiconductor layer33. In this manner, the second trench 13 is the contact part forcontacting the n⁺-type semiconductor layer 32 and the p⁺-typesemiconductor layer 33.

In addition, the first metal film 27 covers the surface and the gradientsurface of the insulating layer 26, the gradient surface of the oxidefilm 25, the portion of the surface 22A of the semiconductor layer 22 inthe transistor area D not covered by the oxide film 25, the gradientsurface 22C forming the boundary of the diode area C and the transistorarea D on the is semiconductor layer 22, and the surface 22A of thesemiconductor layer 22 in the diode area C. The first metal film 27 isSchottky bonded relative to the surface 22A of the semiconductor layer22 in the diode area C (n⁻-type semiconductor layer 34) and the gradientsurface 22C of the n⁻-type semiconductor layer 34. The gradient surface22C is perpendicular to the surface 22A.

The source electrode 28 contains, for example, Wu. The source electrode28 is embedded in the inner side of the second trench 13 where the firstmetal film 27 is formed on the inner surface thereof.

The second metal film 29 contains Ti or TiN, and covers the entiresurface (the upper surface in FIG. 5) of the first metal film 27 and thesurface of the source electrode 28 exposed from the second trench 13.

The wiring layer 30 contains, for example, an AlCu alloy. The wiringlayer 30 is stacked on the second metal film 29 and covers the entiresurface (the upper surface in FIG. 5) of the second metal film 29. Thewiring layer 30 is electrically connected to the corresponding externalelectrode among the plurality of external electrodes 2 (see FIG. 1 andFIG. 2). The gate electrode 24 is electrically connected to thecorresponding external electrode 2 by a switching wiring, which is notshown.

In the transistor area D, the wiring layer 30, the second metal film 29,the source electrode 28, the first metal film 27, the n⁺-typesemiconductor layer 32 and the p⁺-type semiconductor layer 33 areelectrically connected. The back surface electrode 21, the semiconductorsubstrate 20, the n⁻-type semiconductor layer 34 closer to thesemiconductor substrate 20 as compared with the p⁻-type semiconductorlayer 31 on the semiconductor layer 22 are electrically connected.

In this way, in the transistor area D, every transistor unit 11A isconstituted. In the transistor unit 11A, the p⁻-type semiconductor layer31 is the main area, the semiconductor substrate 20 and the n⁻-typesemiconductor layer 34 are the drain area, and the n⁺-type semiconductorlayer 32 is the source area. The transistor unit 11A (transistor 11) hasthe first trench 12 in which the gate electrode 24 is embedded, so thetransistor unit 11A is the trench gate-type MOSFET (Metal OxideSemiconductor Field Effect Transistor). In the transistor unit 11A, aparasitic diode is constituted by the p⁻-type semiconductor layer 31 andthe n⁻-type semiconductor layer 34.

For example, in the situation where the source electrode 28 (wiringlayer 30) is grounded and a positive voltage is applied on the backsurface electrode 21, a voltage higher than a threshold is applied onthe gate electrode 24. In this manner, a channel is formed in a channelarea X around the interface of the p⁻-type semiconductor layer 31 andthe gate insulating film 23 on the outer side of the gate electrode 24,and allows the current to pass therethrough from the back surfaceelectrode 21 to the source electrode 28.

In the diode area C, the back surface electrode 21 is in ohmic contactwith the semiconductor substrate 20, and the first metal film 27 isSchottky bonded with the surface 22A and the gradient surface 22C of thesemiconductor layer 22, thereby constituting the Schottky barrier diode10.

The smaller the interval Q between the surface 22A and the back surface22B of the semiconductor layer 22 in the diode area C is, the larger thedifference between the interval Q and the interval P between the surface22A and the back surface 22B of the semiconductor layer 22 in thetransistor area D will be. In this situation, the DC resistance of thesemiconductor layer 22 of the Schottky barrier diode 10 is reduced, andthe Schottky bonding surface of the gradient surface 22C is enlarged,thus reducing the forward voltage of the Schottky barrier diode 10 andimproving the performance of the Schottky barrier diode 10. However, toensure the minimum level of the withstand voltage of the Schottkybarrier diode 10, the interval Q preferably is 2.5 μm or more.

FIG. 6A to FIG. 6M are illustrative cross-sectional views of afabricating method of the semiconductor device in FIG. 5.

Firstly, as shown in FIG. 6A, the semiconductor substrate 20 isfabricated in a method commonly known in this field.

Next, as shown in FIG. 6B, the epitaxial growth is carried out on thesurface of the semiconductor substrate 20, thus forming thesemiconductor layer 22 on the semiconductor substrate 20.

Subsequently, an ion implantation of a p-type foreign matter (e.g. B) iscarried out on the surface portion of the semiconductor layer 22. Then,the p-type foreign matter is activated by an annealing process, as shownin FIG. 6C, the p⁻-type semiconductor layer 31 is formed on the surfaceportion of the semiconductor layer 22. The portion closer to thesemiconductor substrate 20 as compared with the p⁻-type semiconductorlayer 31 on the semiconductor layer 22 is the n⁻-type semiconductorlayer 34.

After that, a selective ion implantation of an n-type foreign matter(e.g. PAs) is carried out on the surface portion of the p⁻-typesemiconductor layer 31. Then, the n-type foreign matter is activated bythe annealing process, as shown in FIG. 6D, the n⁺-type semiconductorlayer 32 is formed on the surface portion of the p⁻-type semiconductorlayer 31.

Thereafter, an etching process is carried out with the anticorrosiveagent pattern (not shown) as the mask so as to dig from the surface 22Aof the semiconductor layer 22. As shown in FIG. 6E, a recessed portion35 is recessed from the back surface 22B on the semiconductor layer 22in the diode area C. The first trench 12 is formed on the semiconductorlayer 22 in the transistor area D. The bottom 35A of the recessedportion 35 and the bottom 12A of the first trench 12 are located at thesame position in the thickness direction of the semiconductor layer 22and in the same plane.

Then, the SiO₂-containing gate insulating film 23 is formed on theentire inner surface of the first trench 12 by e.g. a CVD (ChemicalVapor Deposition) process as shown in FIG. 6F.

Afterwards, a polysilicon-containing gate electrode 24 is embedded inthe inner side of the gate insulating film 23 of the first trench 12 asshown in FIG. 6G.

Then, a SiO₂-containing film (SiO₂ film) 36 is formed on the surface 22Aof the semiconductor layer 22 in the diode area C and the transistorarea D and the entire area of the gradient surface 22C of thesemiconductor layer 22 on the boundary in the diode area C and thetransistor area D by, for example, the CVD process as shown in FIG. 6H.

Then, the glass layer (glass layer) 37 that contains BPSG is stacked onthe SiO₂ film 36 by means of, for example, the high density CVD processas shown in FIG. 6I.

Subsequently, an etching process is carried out with the anticorrosiveagent pattern (not shown) as the mask so as to sequentially dig theglass layer 37, the SiO₂ film 36 and the semiconductor layer 22 in thetransistor area D. The second trench 13 is thus formed in the transistorarea D as shown in FIG. 6J.

Next, a selective ion implantation of the p-type foreign matter (e.g. B)is carried out on the surface of the semiconductor layer 22 through thesecond trench 13. Then, the p-type foreign matter is activated by theannealing process as shown in FIG. 6K, the p⁺-type semiconductor layer33 is formed on the area around the second trench 13 of the p⁻-typesemiconductor layer 31.

Subsequently, an etching process is carried out with the anticorrosiveagent pattern (not shown) as the mask so as to selectively remove theSiO₂ film 36 and the glass layer 37, as shown in FIG. 6L, and theresidues of the SiO₂ film 36 and the glass layer 37 are left in thetransistor area D. The residual SiO₂ film 36 is the oxide film 25, andthe residual glass layer 37 is the insulating layer 26.

Afterwards, as shown in FIG. 6M, a Ti-containing first metal film 27 isformed on the entire inner surface of the second trench 13, the surfaceand gradient surface of the insulating layer 26, and the entire areaexposed by the gradient surface of the oxide film 25 and the surface 22Aand the gradient surface 22C of the semiconductor layer 22 in thetransistor area D and the diode area C.

Then, a Wu-containing source electrode 28 is embedded in the inner sideof the first metal film 27 of the second trench 13.

After that, a Ti-containing second metal film 29 is formed on the entiresurface of the first metal film 27 and on the surface of the sourceelectrode 28 exposed from the second trench 13. In addition, anAl-containing wiring layer 30 is stacked on the second metal film 29.After a back surface electrode 21 is formed on the back surface of thesemiconductor substrate 20, the semiconductor device 1 as shown in FIG.5 is finished. Furthermore, in this embodiment, the first trench 12 isformed simultaneously when forming the recessed portion 35 (see FIG.6E); but this is only an example, and the fabricating steps may bealtered. For example, the second trench 13 (see FIG. 6J) is formedsimultaneously when forming the recessed portion 35.

FIG. 7 and FIG. 8 are illustrative cross-sectional views of asemiconductor device according to the other embodiment of the presentinvention.

Hereinafter, some other embodiments different from the above embodimentare illustrated, wherein the same parts in the following embodimentsthat correspond to the above embodiment are given the same referencenumerals, and the details of the description of the same parts areomitted. In both FIG. 7 and FIG. 8, when observed from the top, thetransistor area D surrounds the diode area C (see FIG. 1 and FIG. 2).

The semiconductor device 1 in FIG. 7 similar to the above embodimentalso includes the trench gate-type MOSFET, but does not have the secondtrench 13 (see FIG. 5).

The semiconductor device 1 in FIG. 7 has a semiconductor substrate 20, aback surface electrode 21, a semiconductor layer 22, a gate insulatingfilm 23 and a gate electrode 24, an insulating layer 40 and a metal film41.

The semiconductor substrate 20 contains the n⁺-type semiconductor. Theback surface electrode 21 covers the entire back surface (FIG. 7 thelower surface in FIG. 7) of the semiconductor substrate 20, and is inohmic contact with the back surface of the semiconductor substrate 20.

The semiconductor layer 22 is epitaxially grown and stacked on thesurface of the semiconductor substrate 20 (the upper surface in FIG. 7).The semiconductor layer 22 contains an n⁻-type semiconductor having aconcentration lower than the semiconductor substrate 20. In thesemiconductor layer 22 in FIG. 7, the upper surface is referred to asthe surface 22A, and the lower surface is referred to as the backsurface 22B.

FIG. 7 illustrates the semiconductor layer 22 near the boundary of thediode area C and the transistor area D. The semiconductor layer 22 inthe diode area C is thinner than the semiconductor layer 22 in thetransistor area D. Therefore, the surface 22A of the semiconductor layer22 in the diode area C is located at a deep position closer to thesemiconductor substrate 20 as compared with the surface 22A of thesemiconductor layer 22 in the transistor area D. Therefore, the surface22A of the semiconductor layer 22 is recessed towards the semiconductorsubstrate 20 in the diode area C. The interval P between the surface 22Aand the back surface 22B of the semiconductor layer 22 in the transistorarea D is larger than the interval Q between the surface 22A and theback surface 22B of the semiconductor layer 22 in the diode area C. Thethickness of the semiconductor layer 22 in the diode area C is 2.5 μm ormore.

The p⁻-type semiconductor layer 31 is formed on the entire surface ofthe semiconductor layer 22 in the transistor area D. The n⁺-typesemiconductor layer 32 is selectively formed on the surface portion ofthe p⁻-type semiconductor layer 31. The surface of the n⁺-typesemiconductor layer 32 and the surface area of the p⁻-type semiconductorlayer 31 where the n⁺-type semiconductor layer 32 is not formed are inthe same plane, thus forming the surface 22A of the semiconductor layer22 in the transistor area D.

The first trench 12 having the depth of 1 μm or more is formed on thesemiconductor layer 22 in the transistor area D. The first trench 12 isdug from the surface 22A to the back surface 22B of the semiconductorlayer 22 in the transistor area D. The first trench 12 penetratesthrough the p⁻-type semiconductor layer 31 at the position adjacent tothe n⁺-type semiconductor layer 32, to reach the middle of the area(referred to as the n⁻-type semiconductor layer 42) closer to the backsurface 22B as compared with the p⁻-type semiconductor layer 31 of thesemiconductor layer 22. The interval R between the bottom 12A of thefirst trench 12 and the back surface 22B of the semiconductor layer 22is smaller than the interval P, and is equal to the interval Q. In otherwords, the bottom 12A of the first trench 12 and the surface 22A of thesemiconductor layer 22 in the diode area C are located at the sameposition in the thickness direction of the semiconductor layer 22 andare located in the same plane.

The gate insulating film 23 contains SiO₂ and is formed on the entireinner surface of the first trench 12.

The gate electrode 24 contains polysilicon and is embedded in the innerside of the gate insulating film 23 of the first trench 12.

The insulating layer 40 contains SiO₂, and selectively covers thesurface 22A of the semiconductor layer 22 in the transistor area D. Theinsulating layer 40 covers the entire surface of the gate electrode 24protruding from the surface 22A of the semiconductor layer 22 (the uppersurface in FIG. 7), and is connected with the gate insulating film 23around the gate electrode 24, and meanwhile contacts the surfaceportions of the n⁺-type semiconductor layer 32 and the p⁻-typesemiconductor layer 31 around the first trench 12.

The metal film 41 contains a Schottky bonded metal (Ti, Mo, Pd or TiN)formed by bonding with the n⁻-type silicon. The metal film 41 covers theentire surface 22A of the respective semiconductor layer 22 in the diodearea C and the transistor area D and the entire area of the gradientsurface 22C forming the boundary of the diode area C and the transistorarea D on the semiconductor layer 22. The metal film 41 is Schottkybonded with the surface 22A and the gradient surface 22C of thesemiconductor layer 22 in the diode area C (n⁻-type semiconductor layer42). The metal film 41 is electrically connected with correspondingexternal electrodes among the plurality of external electrodes 2 (seeFIG. 1 and FIG. 2). The gate electrode 24 is electrically connected withthe corresponding external electrode 2 by a switching wiring which isnot shown.

In the semiconductor device 1, the metal film 41, the p⁻-typesemiconductor layer 31, and the n⁺-type semiconductor layer 32 areelectrically connected. The back surface electrode 21, the semiconductorsubstrate 20, and the n⁻-type semiconductor layer 42 on thesemiconductor layer 22 closer to the semiconductor substrate 20 ascompared with the p⁻-type semiconductor layer 31 are electricallyconnected.

The n⁻-type semiconductor layer 42 becomes the drain area. The n⁺-typesemiconductor layer 32 becomes the source area. The p⁻-typesemiconductor layer 31 becomes the main area. A parasitic diode isconstituted by the p⁻-type semiconductor layer 31 and the n⁻-typesemiconductor layer 42 in the transistor unit 11A.

For example, in the situation that the metal film 41 is grounded and thepositive voltage is applied on the back surface electrode 21, a voltagehigher than a threshold is applied on the gate electrode 24. In thismanner, a channel is formed in a channel area X around the interface ofthe p⁻-type semiconductor layer 31 and the gate insulating film 23 onthe outer side of the gate electrode 24, and allows the current to passtherethrough from the back surface electrode 21 to the metal film 41.

In the diode area C, the back surface electrode 21 is in ohmic contactwith the semiconductor substrate 20, and the metal film 41 is Schottkybonded with the surface 22A of the semiconductor layer 22, therebyconstituting the Schottky barrier diode 10.

The transistor 11 (transistor unit 11A) of the semiconductor device 1 inFIG. 8 is a planar MOSFET different from this embodiment, and does nothave the first trench 12 (see FIG. 5 and FIG. 7).

The semiconductor device 1 in FIG. 8 has a semiconductor substrate 20, aback surface electrode 21 and a semiconductor layer 22, a gateinsulating film 50, a gate electrode 51, an insulating film 52 and ametal film 53.

The semiconductor substrate 20 contains the n⁺-type semiconductor. Theback surface electrode 21 covers the entire back surface (the lowersurface in FIG. 8) of the semiconductor substrate 20, and is in ohmiccontact with the back surface of the semiconductor substrate 20.

The semiconductor layer 22 is epitaxially grown and stacked on thesurface of the semiconductor substrate 20 (the upper surface in FIG. 8).The semiconductor layer 22 contains an n⁻-type semiconductor having aconcentration lower than the semiconductor substrate 20. In thesemiconductor layer 22 in FIG. 8, the upper surface is referred to asthe surface 22A, and the lower surface is referred to as the backsurface 22B.

FIG. 8 illustrates the semiconductor layer 22 near the boundary of thediode area C and the transistor area D. The semiconductor layer 22 inthe diode area C is thinner than the semiconductor layer 22 in thetransistor area D. Therefore, the semiconductor layer 22 in the diodearea C is located at a deep position closer to the semiconductorsubstrate 20 as compared with the surface 22A of the semiconductor layer22 in the transistor area D. Therefore, the surface 22A of thesemiconductor layer 22 is recessed towards the semiconductor substrate20 in the diode area C. The interval P between the surface 22A and theback surface 22B of the semiconductor layer 22 in the transistor area Dis larger than the interval Q between the surface 22A and the backsurface 22B of the semiconductor layer 22 in the diode area C. Thesemiconductor layer 22 in the diode area C is 2.5 μm thick or more.

The p⁻-type semiconductor layer 54 is selectively formed on the surfaceportion of the semiconductor layer 22 in the transistor area D. Aplurality of p⁻-type semiconductor layers 54 is formed, and isdiscretely configured on the surface portion of the semiconductor layer22. The n⁺-type semiconductor layer 55 is formed on the surface portionof each p⁻-type semiconductor layer 54. The surface of the n⁺-typesemiconductor layer 55 and the surface area of the p⁻-type semiconductorlayer 54 where the n⁺-type semiconductor layer 55 is not formed are inthe same plane, thus forming the surface 22A of the semiconductor layer22 in the transistor area D.

The gate insulating film 50 contains SiO₂, and partially covers thesurface 22A of the semiconductor layer 22 in the transistor area D. Thegate insulating film 50 is formed on the surface 22A of thesemiconductor layer 22 in the transistor area D at an interval and spansthe adjacent n⁺-type semiconductor layers 55.

The gate electrode 51 contains, for example, polysilicon, and is stackedon the gate insulating film 50.

The insulating film 52 contains SiO₂. The insulating film 52 covers theentire surface portion of the gate electrode 51 which is not in contactwith the gate insulating film 50. The insulating film 52 and the gateinsulating film 50 are connected.

The metal film 53 contains a Schottky bonded metal (Ti, Mo, Pd or TiSi)formed by bonding with the n⁻-type silicon. The metal film 53 covers theinsulating film 52, the entire surface 22A of the respectivesemiconductor layer 22 in the diode area C and the transistor area D,and the entire area of the gradient surface 22C forming the boundary ofthe diode area C and the transistor area D of the semiconductor layer22. The metal film 53 is Schottky bonded with the surface 22A and thegradient surface 22C of the semiconductor layer 22 in the diode area C(strictly referred to as the following n⁻-type semiconductor layer 56).The metal film 53 is electrically connected with corresponding externalelectrodes among the plurality of external electrodes 2 (see FIG. 1 andFIG. 2). The gate electrode 51 is electrically connected with thecorresponding external electrode 2 by a switching wiring which is notshown.

In the semiconductor device 1, the metal film 53, the p⁻-typesemiconductor layer 54, and the n⁺-type semiconductor layer 55 areelectrically connected. The back surface electrode 21, the semiconductorsubstrate 20, and the portion of the semiconductor layer 22 where thep⁻-type semiconductor layer 54 and n⁺-type semiconductor layer 55(referred to as the n⁻-type semiconductor layer 56) are not formed areelectrically connected.

Therefore, a plurality of the transistor units 11A is constituted in thetransistor area D. The semiconductor substrate 20 and the n⁻-typesemiconductor layer 56 become the drain area. The n⁺-type semiconductorlayer 55 becomes the source area. The p⁻-type semiconductor layer 54becomes the main area. In the transistor unit 11A, the parasitic diodeis constituted by the p⁻-type semiconductor layer 54 and the n⁻-typesemiconductor layer 56.

For example, in the situation that the metal film 53 is grounded and thepositive voltage is applied on the back surface electrode 21, a voltagehigher than a threshold is applied on the gate electrode 51. In thismanner, a channel is formed in a channel area X around the interface ofthe p⁻-type semiconductor layer 54 and the gate insulating film 50 andallows the current to pass therethrough from the back surface electrode21 to the metal film 53.

In the diode area C, the back surface electrode 21 is in ohmic contactwith the semiconductor substrate 20, and the metal film 53 is Schottkybonded with the surface 22A and the gradient surface 22C of thesemiconductor layer 22 (the n⁻-type semiconductor layer 56), therebyconstituting the Schottky barrier diode 10.

FIG. 9 is a schematic perspective view of a semiconductor packageaccording to an embodiment of the present invention.

Referring to FIG. 9, the semiconductor package 60 includes any of theabove semiconductor devices 1, a metal lead frame 61, and a resinpackage 65.

The semiconductor device 1 is bonded on the lead frame 61. The leadframe 61 includes a rectangular flat chip pad 62, leads 63A configuredat an interval on one side of the chip pad 62, and leads 63B extendingout from the other side of the chip pad 62. The number of leads 63A andleads 63B are respectively plural (four each are used herein by way ofexample).

In the semiconductor device 1, the back surface electrode 21 (see FIG.5, FIG. 7 and FIG. 8) is the upper surface bonded on the chip pad 62,and each lead 63A is connected with the corresponding external electrode2 on the surface of the semiconductor device 1 surface by a connectingline 64. The leads 63A ands 63B are thereby electrically connected tothe Schottky barrier diode 10 and transistor 11 in the semiconductordevice 1 (see FIG. 1 and FIG. 2). In FIG. 9, the external electrode 2 onthe right end is connected to the gate electrode 24, and anotherexternal electrode 2 is connected to the source electrode 28 (also seeFIG. 5). In this situation, in FIG. 9, the lead 63A on the right end isa gate lead, and the other 3 leads 63A are source leads. All the leads63B are drain leads.

The semiconductor device 1 and the lead frame 61 which are bondedtogether are covered by the resin package 65 in a manner that the leads63A and the leads 63B are exposed. The semiconductor package 60 makesthe leads 63A and the leads 63B opposing to the mounting wiringsubstrate (not shown), and may be connected (mounted) to the mountingwiring substrate.

FIG. 10 is a circuit diagram of a DC-DC converter adopting thesemiconductor device of the present invention.

In the DC-DC converter 100 of FIG. 10, a control portion (IC) 91 isconnected with a highside transistor 92 and a lowside transistor 93. Thesemiconductor device 1 of the present invention may be used as thelowside transistor 93. In this situation, the transistor 11 of thesemiconductor device 1 becomes the lowside transistor 93, and theSchottky barrier diode 10 connects the transistor 92 and the lowsidetransistor 93

As described above, in the semiconductor device 1, the semiconductorlayer 22 in the diode area C is thinner than the semiconductor layer 22in the transistor area D (see FIG. 5, FIG. 7 and FIG. 8). In thismanner, in the transistor area D, the thickness of the semiconductorlayer 22 may be set to the necessary thickness for ensuring thewithstand voltage of the transistor 11 (every transistor unit 11A). Onthe other hand, in the diode area C, the thickness of the semiconductorlayer 22 may be set to the minimum necessary level. This allows a DCresistance of the Schottky barrier diode to be reduced, thereby reducingthe forward voltage. In other words, the thickness of the semiconductorlayer 22 in the transistor area D and the diode area C are respectivelyoptimized. Therefore, the present composition of the transistor 11 andthe Schottky barrier diode 10 formed on the chip ensures the withstandvoltage of the transistor 11 and reduces the forward voltage of theSchottky barrier diode 10.

The semiconductor layer 22 in the diode area C is 2.5 μm thick or more,so as to ensure the minimum level withstand voltage of the Schottkybarrier diode 10.

In the trench-type transistor 11 (the transistor unit 11A), the bottom12A of the first trench 12, and the surface 22A of the semiconductorlayer 22 in the diode area C are located at the same position in thethickness direction of the semiconductor layer 22 (see FIG. 5 and FIG.7). Thus, the steps of forming the first trench 12 and polishing thesurface 22A of the semiconductor layer 22 in the diode area C to makethe semiconductor layer thinner (the step of forming the recessedportion 35) may be carried out in one step (see FIG. 6E). Therefore, thecost of fabricating the semiconductor device 1 may be reduced bydecreasing the number of steps. A cheap and high-performancesemiconductor device 1 can thus be provided.

However, where the number of steps is not a concern, in the thicknessdirection of the semiconductor layer 22, the bottom 12A of the firsttrench 12 indicated by the solid line in FIG. 5 is located at a positionfurther away from a back surface 22B of the semiconductor layer 22 ascompared with the surface 22A of the semiconductor layer 22 in the diodearea C. In this situation, the interval R′ (see FIG. 5) between thebottom 12A of the first trench 12 and the back surface 22B of thesemiconductor layer 22 is larger than the interval Q between the surface22A and the back surface 22B of the semiconductor layer 22 in the diodearea C.

In the thickness direction of the semiconductor layer 22, the bottom 12Aof the first trench 12 may also be located at a position closer to theback surface 22B of the semiconductor layer 22 as compared with thesurface 22A of the semiconductor layer 22 in the diode area C, asindicated by the dashed line in FIG. 5. In this situation, an intervalR″ (see FIG. 5) between the bottom 12A of the first trench 12 and theback surface 22B of the semiconductor layer 22 is smaller than theinterval Q.

When observed from the top in the thickness direction of thesemiconductor layer 22, the transistor area D surrounds the diode area C(see FIG. 1 to FIG. 4). When the transistor 11 of the transistor area Dis ON, the Schottky barrier diode 10 of the diode area C is OFF, therebyrealizing heat dissipation of the semiconductor layer 22 by using thediode area C. When the transistor 11 is OFF, heat dissipation of thesemiconductor layer 22 may be realized by using the transistor area D.The above manner may prevent the semiconductor device 1 from rising intemperature. In particular, the transistor area D is configured tosurround the diode area C, so as to dissipate the heat of one area byanother area, thereby effectively preventing a rise in temperature ofthe semiconductor device 1. A plurality of diode areas C is scatteredand uniformly distributed at a necessary interval, thus furthereffectively preventing a rise of temperature in the semiconductor device1 (see FIG. 1 and FIG. 2).

The above-described embodiments of the present invention are intended tobe illustrative only. Numerous alternative embodiments may be devised bypersons skilled in the art without departing from the scope of thefollowing claims.

1. A semiconductor device, comprising: a semiconductor layer; atransistor area, formed on the semiconductor layer to constitute atransistor; and a diode area, formed on the semiconductor layer toconstitute a Schottky barrier diode; wherein the semiconductor layer inthe diode area is thinner than the semiconductor layer in the transistorarea.
 2. The semiconductor device according to claim 1, wherein thesemiconductor layer in the diode area is 1 μm or more thinner than thesemiconductor layer in the transistor area.
 3. The semiconductor deviceaccording to claim 1, wherein the thickness of the semiconductor layerin the diode area is 2.5 μm or more.
 4. The semiconductor deviceaccording to claim 1, wherein the transistor is a trench-type transistorhaving a first trench dug from a surface of the semiconductor layer inthe transistor area; and the bottom of the first trench and a surface ofthe semiconductor layer in the diode area are located at the sameposition in a thickness direction of the semiconductor layer.
 5. Thesemiconductor device according to claim 1, wherein the transistor is atrench-type transistor having a first trench dug from a surface of thesemiconductor layer in the transistor area; and in a thickness directionof the semiconductor layer, as compared with a surface of thesemiconductor layer in the diode area, the bottom of the first trench islocated at a position further away from a back surface of thesemiconductor layer.
 6. The semiconductor device according to claim 1,wherein the transistor is a trench-type transistor having a first trenchdug from a surface of the semiconductor layer in the transistor area;and in a thickness direction of the semiconductor layer, as comparedwith a surface of the semiconductor layer in the diode area, the bottomof the first trench is located at a position closer to a back surface ofthe semiconductor layer.
 7. The semiconductor device according to claim4, wherein the depth of the first trench is 1 μm or more.
 8. Thesemiconductor device according to claim 4, further comprising aSiO₂-containing gate insulating film is formed on an inner surface ofthe first trench.
 9. The semiconductor device according to claim 8,further comprising a polysilicon-containing gate electrode is embeddedon an inner side of the gate insulating film of the first trench. 10.The semiconductor device according to claim 4, wherein the transistorcomprises a main area, a drain area and a source area; a second trenchin contact with the source area is formed on the semiconductor layer,and the second trench is dug from the surface of the semiconductor layerin the transistor area; and the surface of the semiconductor layer inthe diode area is located at a position deeper than the bottom of thesecond trench.
 11. The semiconductor device according to claim 10,wherein the first trench and the second trench are alternatelyconfigured as shown in vertical view along the thickness direction ofthe semiconductor layer.
 12. The semiconductor device according to claim11, wherein the first trench and the second trench are stripe-shaped.13. The semiconductor device according to claim 11, wherein the firsttrench is mesh-shaped as a mesh-shaped area on which the second trenchis configured on an inner side thereof.
 14. The semiconductor deviceaccording to claim 1, wherein the transistor is a planar transistor. 15.The semiconductor device according to claim 1, wherein the transistorarea surrounds the diode area as shown in vertical view along thethickness direction of the semiconductor layer.
 16. The semiconductordevice according to claim 1, further comprising a metal film,electrically connected with the transistor and Schottky bonded with thesemiconductor layer in the diode area.
 17. The semiconductor deviceaccording to claim 16, wherein the metal film comprises Ti, Mo, Pd orTiN.
 18. The semiconductor device according to claim 1, wherein thesemiconductor layer is epitaxially grown on a surface of a semiconductorsubstrate.
 19. The semiconductor device according to claim 18, furthercomprising a back surface electrode, in ohmic contact with a backsurface of the semiconductor substrate.
 20. A semiconductor package,comprising: the semiconductor device according to claim 1; and a resinpackage, covering the semiconductor device.